CMOS (complementary metal oxide semiconductor) image sensors and CCD (charge-coupled device) image sensors are known as solid-state imaging devices used in digital cameras and cameras for cellphones. Among those image sensors, CMOS image sensors are image sensors that use MOS transistors to read out signals that correspond to charges stored in photoelectric conversion elements such as photodiodes. In CMOS image sensors, in general, power lines and signal lines for switching are formed over a semiconductor substrate inplural layers (refer to Patent document 1).
In recent years, marked advancements have been made in the pixel size reduction with increase in the number of pixels. How to increase the light collection efficiency is now an important issue. The light collection efficiency can be increased by focusing light entering a solid-state imaging device on photodiodes by means of microlenses. However, the miniaturization of pixels has made the optical designing of microlenses difficult. Furthermore, in CMOS image sensors, if the focal length is increased, incident light is reflected diffusely by a light shield film and wiring layers formed over the photodiodes and resulting reflection light become factors in lowering the uniformity of the sensitivities of the respective pixels. On the other hand, if the focal length is shortened, light comes to shine on portions other than the photodiodes, which makes it difficult to increase the light collection efficiently sufficiently.
In view of the above, Patent document 1 proposes a solid-state imaging device in which ring-shaped metal members which functions as waveguides are formed over photodiodes (over a semiconductor substrate) in the same layer as a wiring layer. These ring-shaped metal members are not in contact with the semiconductor substrate or any other interconnections but are completely buried in an interlayer insulating film. This solid-state imaging device makes it possible to manufacture a solid-state imaging device that is high in light collection efficiently at a low cost because waveguides can be formed by the same process as interconnections.